In recent years, it has become clear that the majority of cell surface markers are shared by many types of stem and progenitor cells. Thus the ability to separate unique cell sub-populations using current methods is limited. Although it is known that stem cells secrete specific factors into the extracellular space, it is difficult to characterize secretory activity of individual viable cells within a heterogeneous population. Association of the secreted factor(s) with a specific cell type provides an additional marker that can be used to characterize the cell and permit separation of cells while maintaining viability. Combining immunophenotyping with secretory profile is powerful approach for both research and eventual therapeutic applications. Development of new, reliable methods for analyzing and recovering single, viable stem cells based on secretory profile combined with expression of cell surface antigens is of considerable interest. The GMD Stem Cell Assay addresses the need for a functional, multiparameter, single cell assay that does not compromise cell viability, physiological state, and functionality. Phase I research optimized the assay for use with several experimental hematopoietic models. Phase II research will expand use of the assay with other models, including endothelial progenitor cells. This assay format can be widely used for immunological studies, including stem cell research and clinical applications. By providing a reliable method for analyzing and recovering single, viable stem cells based on secretory profile combined with expression of cell surface antigens, this assay format will be useful for stem cell research and clinical applications. [unreadable] [unreadable] [unreadable]